Buggy code:
; static final char [ ] charArray_t = new char [ ] { 't' } ; static final char [ ] charArray_u = new char [ ] { 'u' } ; static final char [ ] charArray_v = new char [ ] { 'v' } ; static final char [ ] charArray_w = new char [ ] { 'w' } ; static final char [ ] charArray_x = new char [ ] { 'x' } ; static final char [ ] charArray_y = new char [ ] { 'y' } ; static final char [ ] charArray_z = new char [ ] { 'z' } ; static final char [ ] initCharArray = new char [ ] { '' , '' , '' , '' , '' , '' } ; static final int TableSize = 30 ; static final int InternalTableSize = 6 ; public static final int OptimizedLength = 6 ; public final char [ ] [ ] [ ] [ ] charArray_length = new char [ Scanner . OptimizedLength ] [ Scanner . TableSize ] [ Scanner . InternalTableSize ] [ ] ; int currentLineNr = - 1 ; int previousLineNr = - 1 ; NLSLine currentLine = null ; public static final String TAG_PREFIX = "////$NON-NLS-" ; public static final int TAG_PREFIX_LENGTH = Scanner . TAG_PREFIX . length ( ) ; public static final String TAG_POSTFIX = "$" ; public static final int TAG_POSTFIX_LENGTH = Scanner . TAG_POSTFIX . length ( ) ; public StringLiteral [ ] nonNLSStrings = null ; public boolean checkNonExternalizedStringLiterals = false ; public boolean wasNonExternalizedStringLiteral = false ; static int newEntry2 = 0 ; static int newEntry3 = 0 ; static int newEntry4 = 0 ; static int newEntry5 = 0 ; static int newEntry6 = 0 ; public static final int RoundBracket = 0 ; public static final int SquareBracket = 1 ; public static final int CurlyBracket = 2 ; public static final int BracketKinds = 3 ; public Scanner ( ) { } public Scanner ( boolean tokenizeComments , boolean tokenizeWhiteSpace , boolean checkNonExternalizedStringLiterals , long sourceLevel , char [ ] [ ] taskTags , char [ ] [ ] taskPriorities ) { } public final boolean atEnd ( ) { } private void checkNonExternalizedString ( ) throws InvalidInputException { } public void checkTaskTag ( int commentStart , int commentEnd ) { } public char [ ] getCurrentIdentifierSource ( ) { } public int getCurrentTokenEndPosition ( ) { } public final char [ ] getCurrentTokenSource ( ) { } public final char [ ] getCurrentTokenSourceString ( ) { } public final char [ ] getRawTokenSource ( ) { } public int getCurrentTokenStartPosition ( ) { } public final int getLineEnd ( int lineNumber ) { } public final int [ ] getLineEnds ( ) { } public final int getLineStart ( int lineNumber ) { } public final boolean getNextChar ( char testedChar ) { } public final int getNextChar ( char testedChar1 , char testedChar2 ) { } public final boolean getNextCharAsDigit ( ) { } public final boolean getNextCharAsDigit ( int radix ) { } public boolean getNextCharAsJavaIdentifierPart ( ) { } public int getNextToken ( ) throws InvalidInputException { } public final void getNextUnicodeChar ( ) throws IndexOutOfBoundsException , InvalidInputException { } public char [ ] getSource ( ) { } public final void jumpOverMethodBody ( ) { } public final boolean jumpOverUnicodeWhiteSpace ( ) throws InvalidInputException { } final char [ ] optimizedCurrentTokenSource1 ( ) { } final char [ ] optimizedCurrentTokenSource2 ( ) { } final char [ ] optimizedCurrentTokenSource3 ( ) { } final char [ ] optimizedCurrentTokenSource4 ( ) { } final char [ ] optimizedCurrentTokenSource5 ( ) { } final char [ ] optimizedCurrentTokenSource6 ( ) { } private void parseTags ( NLSLine line ) throws InvalidInputException { } public final void pushLineSeparator ( ) throws InvalidInputException { } public final void pushUnicodeLineSeparator ( ) { } public final void recordComment ( boolean isJavadoc ) { } public void resetTo ( int begin , int end ) { } public final void scanEscapeCharacter ( ) throws InvalidInputException { } public int scanIdentifierOrKeyword ( ) throws InvalidInputException { } public int scanNumber ( boolean dotPrefix ) throws InvalidInputException { } public final int getLineNumber ( int position ) { } public final void setSource ( char [ ] source ) { } public String toString ( ) { if ( ( startPosition ) == ( source . length ) ) return "EOF\n\n" + ( new String ( source ) ) ; if ( ( currentPosition ) > ( source . length ) ) <START_BUG> return "behind<seq2seq4repair_space>the<seq2seq4repair_space>EOF<seq2seq4repair_space>:-(<seq2seq4repair_space>....\n\n" + ( new String ( source ) ) ; <END_BUG> char [ ] front = new char [ startPosition ] ; System . arraycopy ( source , 0 , front , 0 , startPosition ) ; int middleLength = ( ( ( currentPosition ) - 1 ) - ( startPosition ) ) + 1 ; char [ ] middle ; if ( middleLength > ( - 1 ) ) { middle = new char [ middleLength ] ; System . arraycopy ( source , startPosition , middle , 0 , middleLength ) ; } else { middle = CharOperation . NO_CHAR ; } char [ ] end = new char [ ( source . length ) - ( ( currentPosition ) - 1 ) ] ; System . arraycopy ( source , ( ( ( currentPosition ) - 1 ) + 1 ) , end , 0 , ( ( ( source . length ) - ( ( currentPosition ) - 1 ) ) - 1 ) ) ; return ( ( ( ( new String ( front ) ) + "\n===============================\nStarts<seq2seq4repair_space>here<seq2seq4repair_space>-->" ) + ( new String ( middle ) ) ) + "<--<seq2seq4repair_space>Ends<seq2seq4repair_space>here\n===============================\n" ) + ( new String ( end ) ) ; } public final String toStringAction ( int act ) { } }

Fix:
return "behind<seq2seq4repair_space>the<seq2seq4repair_space>EOF\n\n" + ( new String ( source ) ) ;